DEVICES AND METHODS FOR IMPROVING ACCURACY OF FLUID DELIVERY
Devices and methods for delivering therapeutic fluid to a patient's body are described. The devices may comprise a dispensing unit having a reservoir, a driving mechanism having a movable member for delivering therapeutic fluid to a patient's body, at least one sensor for sensing a relative position of the movable member and generating a signal, and a processor for controlling the driving mechanism to deliver an amount of therapeutic fluid that compensates for a change in the flow of the therapeutic fluid occurring during fluid delivery. The methods may be implemented by operating the driving mechanism, receiving a signal based on the position of the movable member, determining an amount of therapeutic fluid to deliver, and controlling the driving mechanism to deliver an amount of fluid that compensates for a change in flow occurring during fluid delivery.
The present invention claims priority to U.S. Provisional Patent Application No. 61/069,297, entitled “Systems and Methods for Improving Accuracy of Fluid Delivery,” filed on Mar. 12, 2008, the disclosure of which is incorporated herein by reference in its entirety.
FIELDDevices and methods for sustained medical infusion of fluids are described herein. In particular, an ambulatory infusion device that can be attached to the patient's body and dispense accurate doses of fluids to the patient's body is provided. More particularly, a skin adherable infusion device that may employ a peristaltic metering mechanism and a method for improving fluid delivery accuracy are described herein. The term “fluid” refers to any therapeutic fluid, including but not limited to insulin.
BACKGROUNDMedical treatment of several illnesses requires continuous drug infusion into various body compartments via subcutaneous or intra-venous injections. Diabetes mellitus patients, for example, require administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory insulin infusion pumps have emerged as a superior alternative to multiple daily syringe injections of insulin. These pumps, which deliver insulin at a continuous basal rate as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections, and allow them to maintain almost normal routines. Delivered volumes must be precise and in accordance with a programmed delivery schedule because an overdose or under-dose of insulin could be fatal.
Several conventional ambulatory insulin infusion devices are currently available on the market. One configuration of these devices relates to a miniature skin adherable infusion device, also referred to as a “dispensing patch”. It is lightweight, small in size (discreet), and has no tubing. Some dispensing patches use peristaltic metering mechanisms. An example of such a dispensing patch is disclosed in the co-owned, co-pending U.S. patent application Ser. No. 11/397,115 and International Patent Application No. PCT/IL06/001276, the disclosures of which are incorporated herein by reference in their entireties. Other dispensing patches may employ syringe pumps, examples of which are disclosed in co-owned, co-pending International Patent Application No. PCT/IL2008/000641, filed May 11, 2008 and entitled “A Positive Displacement Pump” and U.S. Provisional Patent Application No. 61/123,509, filed Apr. 9, 2008 and entitled “Systems, Devices and Methods for Fluid Delivery”, the disclosures of which are incorporated herein by reference in their entireties.
A peristaltic mechanism typically includes a rotary wheel with rollers and a flexible delivery tube. The rotary wheel with rollers periodically squeezes the flexible tube and delivers the fluid in the direction of rotation of the rotary wheel. A stator provides a counter force against the rotary wheel and has a groove designed to hold the tube in place. The spring-loaded stator can change its position in relation to the rotary wheel. A revolution counter alerts the patient in cases of electro-mechanical dissociation, as disclosed in the co-owned, co-pending International Patent Application No. PCT/IL08/000,642, filed May 11, 2008, and entitled “Methods and Apparatus for Monitoring Rotation of an Infusion Pump Driving Mechanism,” the disclosure of which is incorporated herein by reference in its entirety.
The use of a peristaltic mechanism maintains fluid sterility because the rotary wheel only touches the outer surface of the delivery tube, avoids pressure fluctuations because the delivery tube is continuously squeezed, and eliminates the need for a check valve.
Typically, an accurate and constant flow rate is to be delivered into the body of a user. However, some pumping mechanisms, such as a peristaltic pumping mechanism, have a variable flow rate, thus limiting the pumping mechanism as applied to ambulatory insulin infusion pumps. The peristaltic mechanism delivers the fluid in a series of pulses or surges, also referred to as a pulsation. During a rotary wheel cycle, the flow rate changes according to the relative position of the rollers and the stator. Moreover, no flow or backflow occurs when each roller disengages the stator. These pulsations are of no consequence to most applications, but their influence is significant when a low flow rate is needed, such as for example, during basal insulin delivery by a portable pump. The pulsation frequency is equal to the frequency of passing of successive rollers in contact with the delivery tube causing to a variable ratio between the amount of fluid delivered and the relative position of the pumping mechanism. This may cause inaccuracies and variation, especially when the pumping mechanism is activated without completing a full period, such as for example during low basal delivery. And when the dispensing device is operated according to the pumping mechanism periods, the ability to control and program the fluid delivery schedule is reduced and the effectiveness of the therapeutic treatment may be hampered. Referring to a peristaltic pumping mechanism as an example, the volume delivered by the change of the relative position of the rotary wheel (also referred to as a “flow rate”) may be affected by various parameters, including the delivery tube's mechanical characteristics (e.g., inner and outer diameters and polymer characterization), the rotary wheel diameter, the number of rollers, the stator's diameter, and the stator's spring. The flow rate can also be influenced by other moving parts of the peristaltic pumping mechanism, including without limitation, gears, the shaft, the motor, the steady stator, and the spring-loaded stator.
Conventional systems use mechanical means to reduce pulsations. An example of such mechanical means is discussed in U.S. Pat. No. 6,099,272 to Armstrong et al., which discloses a torque control cam that increases the minimal torque provided by the pump. In addition, U.S. Pat. No. 4,568,255 to Lavender et al. discloses elongated sloped-sweep vanes that increase pressure on the tube. Both mechanisms require high energy, a large motor and a powerful battery.
The reliability of an infusion pump can be enhanced by monitoring the flow rate of the therapeutic fluid. Conventional flow meters employed in infusion pumps are heavy and bulky and cannot precisely monitor low flow volumes. In other words, they do not allow accurate monitoring of the flow rate. An example of such a measurement mechanism is disclosed in International Patent Application No. PCT/US2002/038822 to Sage et al., wherein flow is monitored by optically detecting changes of the fluid refraction index caused by artificially-induced heat. This method is inaccurate for monitoring low flow rates and therefore cannot prevent potential deterioration of the therapeutic fluid or other fluid delivered to the body.
SUMMARYDevices and methods that may employ a pumping mechanism (e.g., peristaltic pump or syringe pump) having a dispensing unit and means for monitoring and controlling the volume of therapeutic fluid being delivered are disclosed. In some embodiments, the dispensing unit may secured to the user's body (e.g., skin adherable). The dispensing unit may be composed of two parts: a disposable part and a reusable part. The dispensing unit may include one or more monitoring means for determining and providing the relative position of one or more movable components of the dispensing unit. A movable component may include but is not limited to a motor, gear, shaft, rotary wheel, roller, plunger, encoder, stator, or cogwheel. A sensor may be positioned on at least one movable component and may include an encoder wheel, at least one light-emitting source (e.g., a light-emitting diode, or LED), and at least one light detector. There is also provided a processor that receives one or more sensor inputs and controls a motor in accordance with those inputs (i.e., closed-loop feedback) to deliver the required dosage accurately. In some embodiments, the motor is activated to compensate for inaccuracies in the pumping mechanism that result from changing a variable pumping rate to a constant flow rate. In particular, inaccuracies may be caused by pulsations in a peristaltic pumping mechanism, asymmetric components (e.g. gear) or plunger wobble in a syringe pumping mechanism. In some embodiments, the processor can be programmed to compensate for a change in the flow rate. The compensation can be calculated accurately by determining and analyzing the amount of fluid delivered with each displacement of a wheel (e.g., rotation of a rotary wheel, cog wheel, or encoder wheel) or of a plunger or other movable components in various other positive displacement pumps. The change in the flow rate, or the compensation, may correlate to the relative position of the one or more movable components as determined by a sensor.
In some embodiments, the flow rate may vary according to the rotation of a wheel (e.g., a rotary wheel, cog wheel, or encoder wheel). In some embodiments, the compensation may be related to a partial wheel rotation. In some embodiments, the amount of fluid delivered may depend on the initial and final positions of the pumping mechanism and on variable flow parameters.
In some embodiments, the processor can be programmed to compensate for backflow caused by the pulsation of a peristaltic pumping mechanism. The compensation can be calculated accurately by determining and analyzing the amount of fluid delivered with each rotation of a wheel. The compensation may correlate to the position of the wheel's roller relative to the stator. Some embodiments may include simplified adjustments to the number of motor rotations (e.g., every ten full motor rotations require another half rotation).
The fluid delivery device may also include a cradle unit, a cannula cartridge unit (that may be skin adherable), and a remote control unit. In some embodiments, the remote control unit may be a cellular phone, a watch, a personal digital assistance (PDA), an iPod, or any other suitable device. In some embodiments, the cradle unit enables connection and disconnection of the dispensing unit from the user's body.
Some embodiments relate to a portable dispensing unit and a method for monitoring and controlling the flow of the therapeutic fluid being delivered.
Some embodiments relate to a portable dispensing unit that employs a peristaltic mechanism and a feedback control for minimizing pulsation, as well as correction in a situation when there is no flow or backflow.
Some embodiments relate to a portable dispensing unit that employs a peristaltic mechanism and a method for preventing or at least minimizing the occurrence of pulsations, no flow or backflow.
Some embodiments relate to controlling and monitoring the relative position between movable components and steady components of the dispensing unit. More particularly, some embodiments relate to controlling and monitoring the relative angular position between rotating components and steady components of the dispensing unit (i.e., rollers and stator, cogwheels and chassis).
Some embodiments relate to monitoring the amount of delivered fluid by controlling the relative position of movable components.
In some embodiments, the position of the movable components within the pumping mechanism may be sensed by displacement transducers, optical sensors, load cell sensors, capacitive sensing, magnetic sensors, piezoelectric sensors, spring potentiometers, or rotary sensors. In some embodiments, the dispensing unit may include more than one sensor. In some embodiments, position can be sensed continuously or at predetermined phases of the pumping mechanism cycle.
In some embodiments, the amount of delivered fluid is calculated according to the two consecutive positions of the pumping mechanism defining an interval, which are determined according to sensor signals, and determining the amount of fluid delivered during a first portion of the interval and during a second portion of the interval. In some embodiments, the interval is related to the pumping mechanism period. In some embodiments, the ratio between the first portion and the amount of fluid delivered may differ from the ratio between the second portion and the amount of fluid delivered.
The coefficients (k, k′, k″, k′″) can be determined empirically or by calculation. For example, k′ correlates to the inner diameter of the delivery tube (230), and k, k″ and k′″ correlate to the roller and rotary wheel (110) dimensions, as do pi, p2, and p3.
The engagement between each roller (101, 102, 103, 104) and the delivery tube (230) starts at “p0” and ends at “p4,” and as noted above is referred to as the “roller period”. As one cycle of the rotary wheel (110) is equal to 2π, a roller's period is equal to 2π divided by the number of rollers within the rotary wheel (110). For example, the roller period for a single roller in a three-roller rotary wheel (110) is equal 2π/3, thus, p0=0 and p4=2π/3.
The volume delivered, V(p), of the peristaltic, pumping mechanism during roller phase “b” is: k′*(p−p1), when the initial position of the rotary wheel (110) is equal to p1. If the initial position, pi, of the rotary wheel (110) is p0, then fluid is also delivered during roller phase “a”. Hence,
V(p)=k*(p12−p02)+k′*(p−p1) (1)
V(p) during a full roller period of p0 to p4 is thus calculated by summing the volumes delivered during the four phases (“a” to “d”) as follows:
V(p)=k*(p12−p02)+k′*(p−p1)+k″*(p2−p3)+k′″*(p4−p3) (2)
Table 2 provides sample values for parameters shown in Table 1. These values are provided here for illustrative purposes only and are not intended to limit the scope of the disclosure.
V(p) during full roller period using values from Table 2 is:
V(p)=0.1·(0.12−0)+0.23·(1.3−0.1)+0·(1.4−1.3)−0.16·(1.57−1.4)=0.25 [μL] (3)
In some embodiments, the rotary wheel (110) can be provided with three rollers. Thus, the period for each roller is 2π/3. An example of the volume of fluid delivered according to the change of a roller's position and the bounds of each roller phase are shown in Table 3 below. The values illustrated in Table 3 are provided for illustrative purposes only and not intended to limit the scope of the disclosure. Referring to the example shown in Table 3, when a roller moves within phases “a” and “b”, the therapeutic fluid is delivered from the dispensing unit into the patient's body. When a roller is within phase “c”, a backflow occurs, i.e. the therapeutic fluid moves backwards into the dispensing unit, thus reducing the amount of fluid delivered to the patient's body. When a roller moves within phase “d”, there is no flow, i.e. the roller presses the tube and blocks any fluid delivery, and thus may be used as a valve. Referring to the example shown in Table 2, during phases “a” and “b” fluid is delivered to the patient's body, backflow occurs during phase “d”, and the tube is blocked during phase “c”.
V(p) during a full roller period using values from Table 3 is:
V=0.2·sin(0.1−0)+0.2·(1.9−0.1)+0.3·(1.9−2)+0·(2π/3−2)=0.35 μL (4)
-
- provide overlapping signals for higher reliability.
- provide consecutive signals for higher resolution of a rotating component's relative position (p).
ΔV=V(pf)−V(pi) (5)
The total volume delivered by the pump (designated as “Vtotal”) is updated at Step 409 as:
Vtotal=ΔV+V+Vtotal (6)
The process is terminated at Step 410.
of the volume delivered function, V(p), based on a roller's position:
-
- When the fluid is delivered to the patient
-
- When there is no flow
-
- On backflow
VTolerance=0.02 μL
pi=0
Vtotal=0 μL (7)
The dosage (V) to be delivered equals 0.5 μL. Thus, if no backflow occurs, such dosage requires less than half a turn (pf<1.57) of the rotary wheel (110). However, in order to compensate for the backflow, almost a frill turn (1.75π) may be needed. The rotary wheel (110) is rotated until the targeted position pf=2.79 is reached at Step 425, thus, delivering a sufficient amount of fluid (V−(V(pf)−V(pi))≦VTolerance) at Step 423. Afterwards, Steps 428, 430, and 431 (shown in
VTolerance=0.02 μL
Vtotal=127 μL (8)
The dosage (V) to be delivered equals 0.25 μL.
Referring to
Thus, rotary wheel (110) is rotated to position pf=2.09, according to Steps 442 and 445 shown in
and the dosage V had been delivered) are met, as shown in
The flow rate and rotation rate adjustment is also beneficial in reduction or prevention of an occurrence or formation of fibrils, aggregations or precipitations when using therapeutic fluid, such as insulin. This adjustment of rotation rate minimizes the period of time during which the backflowing fluid resides in that portion of the delivery tube (230) positioned between the rotary wheel (110) and the stator (190).
Example embodiments of the devices and methods of the present invention have been described herein. As noted elsewhere, these embodiments have been described for illustrative purposes only and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons of ordinary skill in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the disclosure should not be limited by any of the above-described embodiments but should be defined only in accordance with the following claims and their equivalents.
Claims
1.-28. (canceled)
29. An ambulatory infusion pump for delivering therapeutic fluid to a patient's body, the pump including a dispensing unit comprising:
- a reservoir to retain therapeutic fluid;
- a driving mechanism for delivering therapeutic fluid from the reservoir into a patient's body, the driving mechanism including a movable member that moves when therapeutic fluid is being delivered;
- at least one sensor configured to sense a relative position of the movable member, and generating a corresponding sensor signal; and
- a processor in electrical communication with the at least one sensor and configured with instructions to control the driving mechanism,
- wherein the processor controls the driving mechanism based on the sensor signal and at least one flow characteristic of the therapeutic fluid being delivered such that a compensation amount of therapeutic fluid is delivered to compensate for a change in the flow of therapeutic fluid occurring ring during operation of the driving mechanism.
30. The pump according to claim 29, further comprising a positive displacement pump.
31. The pump according to claim 29, further comprising a syringe and a propelling plunger.
32. The pump according to claim 29, further comprising:
- a rotary wheel rotatable by the driving mechanism and having at least one roller,
- a stator arranged adjacent to the rotary wheel, and
- a delivery tube in fluid communication with the reservoir,
- wherein the delivery tube is disposed between the rotary wheel and the stator such that upon rotation of the rotary wheel, a region of the delivery tube is squeezed between the at least one roller and the stator.
33. The pump according to claim 29, wherein the movable member rotates when therapeutic fluid is delivered, and the at least one sensor monitors the number of rotations of the movable member.
34. The pump according to claim 29, wherein the sensor is selected from the group consisting of an optical sensor, a magnetic sensor, a piezoelectric sensor, and a load cell sensor.
35. The pump according to claim 29, wherein the movable member is selected from the group consisting of an encoder, a shaft, a stator, a gear, a cogwheel, rotary wheel, a roller, and a plunger.
36. The pump according to claim 29, wherein the change in the flow of the therapeutic fluid is periodic.
37. The pump according to claim 32, wherein the at least one roller is configured to continuously squeeze the region of the delivery tube to prevent therapeutic fluid from flowing in a direction towards the reservoir.
38. The pump according to claim 32, wherein the at least one roller comprises four rollers.
39. The pump according to claim 32, wherein an amount of therapeutic fluid delivered through the delivery tube is determined based on a monitored stator load.
40. The pump according to claim 29, wherein the driving mechanism further comprises:
- a motor; and
- at least one gear coupled to the motor, and configured to rotate upon application of power from the motor, the gear rotation being monitored by the at least one sensor;
- wherein during activation of the driving mechanism, the gear is rotated at a variable rate resulting in a substantially constant flow rate of therapeutic fluid delivered to the patient's body.
41. The pump according to claim 29, wherein fluid delivery is monitored by at least two sensors.
42. The pump according to claim 29, wherein the processor is further configured to calculate a target position of the movable member based on the sensor signal and on the at least one flow characteristic of the therapeutic fluid being delivered to the patient.
43. The pump according to claim 29, wherein the processor is configured to control the driving mechanism to deliver therapeutic fluid at a basal rate.
44. The pump according to claim 29, wherein the processor is configured to control the driving mechanism to deliver therapeutic fluid at a rate of less than about 2 units per hour.
45. The pump according to claim 29, wherein:
- the at least one flow characteristic of the therapeutic fluid being delivered includes one or more correlations between the sensor signal and an amount of delivered therapeutic fluid, and
- the amount of delivered therapeutic fluid results from at least one of flow in a forward direction, no flow and backflow.
46. The pump according to claim 29, wherein the driving mechanism, the at least one sensor, and the processor operate in a closed-loop mode.
47. The pump according to claim 29, wherein during operation of the driving mechanism, the flow rate of therapeutic fluid is variable.
48. A method for delivering therapeutic fluid to a patient's body, the method comprising the steps of:
- operating a driving mechanism to deliver therapeutic fluid to a patient, the driving mechanism including a movable member operatively coupled to a motor;
- receiving a sensor signal corresponding to a relative position of the movable member;
- determining amount of therapeutic fluid based on the sensor signal and on at least one flow characteristic of the therapeutic fluid; and
- controlling the driving mechanism to deliver the determined amount of therapeutic fluid to the patient to compensate for a change in the flow of therapeutic fluid occurring during operation of the driving mechanism.
49. The method according to claim 48, wherein operating the driving mechanism is based on comparing the determined amount of therapeutic fluid and a previous amount of therapeutic fluid delivered to the patient.
50. The method according to claim 48, wherein:
- receiving a sensor signal corresponding to the relative position of the movable member comprises: receiving a first sensor signal corresponding to a first position of the movable member of the driving mechanism, and receiving a second signal corresponding to a second position of the movable member; and
- controlling the driving mechanism comprises: adjusting the position of the movable member based on the first sensor signal, the second sensor signal and the at least one flow characteristic of the therapeutic fluid being delivered,
- wherein the at least one flow characteristic varies between receiving the first sensor signal and the second sensor signal.
51. The method according to claim 48, wherein:
- operating the driving mechanism causes periodic delivery of therapeutic fluid; and
- completing a period of the driving mechanism operation results in delivering a first amount of therapeutic fluid.
52. The method according to claim 51, wherein controlling the driving mechanism comprising delivering a second amount of therapeutic fluid, the second amount configured to compensate for a change in flow rate of therapeutic fluid occurring during operation of the driving mechanism.
Type: Application
Filed: Mar 12, 2009
Publication Date: Feb 10, 2011
Patent Grant number: 9446185
Inventors: Ofer Yodfat (Modi'in), Avihoo P. Keret (Kfar Vradim)
Application Number: 12/921,702
International Classification: A61M 5/168 (20060101);